VDL Mode 4/STDMA-a CNS data link

At its tenth Air Navigation Conference (1991), the ICAO endorsed the so-called Communication, Navigation, Surveillance/Air Traffic Management concept, CNS/ATM. This concept envisages the use of data link communications, satellite navigation and automatic dependent surveillance (ADS). The Swedish Civil Aviation Administration (SCAA) has been involved in the technical and operational development of an integrated CNS/ATM since 1990. The system concept is based on the use of GNSS and a time synchronised VHF data link (VDL Mode 4/STDMA). The system is intended to support all elements of CNS. This paper discusses the requirements for an integrated CNS system. It also gives an overview of the VDL mode 4/STDMA system as well as description of on-going trials and standardisation effort within ICAO.